The present invention deals with disc drives. More particularly, the present invention deals with positioning a transducer over a surface of a disc in a disc drive.
A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. A typical disc drive also includes one or more transducers supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducers and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is then decoded by the drive controller to recover the data represented by flux reversals stored on a magnetic disc, and consequently represented in the read signal provided by the data head.
Accurate positioning of the data head over a track on the disc is of great importance in writing data to the disc and reading data from the disc.
Recently, magnetoresistive heads (MR heads) have been implemented as data heads. MR heads are commonly referred to as dual element heads. An MR head has one transducer which is used to write data to the disc, and a separate transducer which is used to read data from the disc (i.e., a write transducer and a read transducer). A write transducer is typically formed using thin film technology, and the read transducer is typically formed using magnetoresistive technology.
There exists an offset between the active magnetic centers of these two elements. In other words, MR heads have a spatial separation between the read and write transducers. Also, because of mask misalignment during manufacturing of an MR head, and other manufacturing and operational parameters, the read transducer and write transducer on a single MR head can be spatially separated from one another to a greater or lesser degree than otherwise desired. Thus, when the MR head is finely positioned over a track during a write operation, that same position is not the ideal track center for the MR head during a read operation. Rather, since the read transducer is spatially separated from the write transducer, the MR head must be radially moved within the track (or repositioned within the track) so that the read transducer is positioned over ideal track center.
The problem of spatial separation is further exacerbated because the skew angle (the angle of the MR head with respect to a track on the disc surface) changes for different zones on the disc. Therefore, the effective spatial separation between the read and write transducers on the MR head also changes across the disc.
Another industry trend which has exacerbated the problem of accurately positioning a read head over a disc surface, is that track densities have been increasing for many years. Increased track densities on a magnetic disc require more accurate and higher resolution positioning.
Each MR head can, however, be characterized. During characterization, the offset between the read and write transducers is determined. The present actuator systems attempt to compensate for this offset by using the voice coil actuator to move (or microjog) the data head to the desired position to compensate for this offset.
However, present actuators do present a number of problems in attempting to finely position or otherwise position a data head over a magnetic disc. Conventional actuators are limited in bandwidth to approximately 500 HZ. Further, because of various frictional parameters in the system, conventional actuators can be unable to follow disturbances as low as 150 HZ.
An actuator arm assembly is provided in a disc drive. The disc drive includes a disc with a surface for storing information and a first actuator for moving the actuator arm assembly relative to the surface of the disc. The actuator arm assembly includes an actuator arm coupled to the first actuator, a load beam coupled to the actuator arm, a suspension coupled to the load beam and an air bearing coupled to the suspension. A transducer is mounted on the air bearing and positioned to access the surface of the disc. A second actuator is coupled to the air bearing and the load beam and is controllable to move the air bearing relative to the surface of the disc and relative to the load beam.